This invention relates to an optical chassis for scanner and particularly to a parallel driving mechanism for the optical chassis to move parallelly during scanning operation.
Scanner is a widely used computer peripheral device that uses an optical chassis for housing the mirrors, lamp, lens set and CCD to scan a document for capturing and converting document image into digital signals for computer process.
FIG. 1 shows a typical conventional scanner optical apparatus which includes a casing 10, an optical chassis 20 and a transmission means 301. The casing 10 is hollow and includes four side walls 12 and a bottom wall 14. In the casing 10, there is a guide rail 16 at one side and a guide rod 18 located parallelly at another side for providing linear moving path to the optical chassis 20.
The optical chassis 20 is mounted with a lamp, several mirrors, a lens set and a charge coupled device (CCD, not shown in the figure) for capturing document image.
The optical chassis 20 further has a roller 22 movable on the guide rail 16, a guide bore 24 slidably holds the guide rod 18 and a clamp 26 located at one end thereof.
The transmission means 30 includes a motor 32 and a belt 34 engaged with the clamp 26. When the motor 30 rotates and drives the belt 34, the optical chassis 20 will be moved reciprocally along the guide rail 16 and guide rod 18 to perform scanning operation.
As the clamp 26 is located at one end of the optical chassis 20, when the moving belt 34 drags the optical chassis 20 through the clamp 26 to move along the guide rail 16 and guide rod 18, a torque will incur to optical chassis 20 and result in skew position. The friction between the guide bore 24 and guide rod 18 will increase. The motion might become rough and tremble between the guide bore 24 and guide rod 18, and between the roller 22 and guide rail 16. All this may have negative impact on scanning quality.
Since the optical chassis 20 is not a homogenous member, its center gravity is difficult to locate precisely. It is therefore difficult to locate a precise dragging point for the clamp. Furthermore, the guide rail 16 and guide rod 18 have different friction coefficient against the roller 22 and guide bore 24, the friction unbalance between the two cannot be totally eliminated. Hence the motion of the optical chassis 20 during scanning operation cannot always be as smooth as desired, which unavoidably impacts scanning quality. There is still room for improvement in the driving mechanism for optical chassis in the scanner.
It is an object of this invention to provide a parallel driving mechanism for scanner that will move the optical chassis horizontally and steadily during scanning operation for obtaining improved scanning quality.
The parallel driving mechanism according to this invention includes a casing, an optical chassis, a linkage member, a screw bar and a driving member.
The casing is hollow and rectangular, and has four side walls and a bottom wall. On one side wall, there is a pair of symmetrical pivotal joints. On the bottom wall, there is a pair of parallel guide rails. The optical chassis has two rollers mounted at two ends for supporting and moving the optical chassis on the guide rails and a pair of symmetrical pivotal joints located on a side wall there of. The linkage member has a pair of upper links pivotally engaged with a pair of lower links at one end thereof. Another ends of the upper and lower links engaged respectively with the pivotal joints at the side wall of the casing and optical chassis. The pivotal engaging joints of the upper and lower links are located respectively on a sleeve which has opposite internal screw threads. The screw bar engaged with the two sleeves and has one end engaged with the driving member. When the driving member rotates the screw bar, the two sleeves will be turned in opposite direction, thus will extend or withdraw the upper and lower links simultaneously. Consequently the optical chassis will be pushed or pulled at the two pivotal joints at the aide wall thereof for moving the optical chassis smoothly and steadily along the guide rails for scanning operation.